The first version (1) returns an object with the parameters currently associated with the distribution object.
The second version (2) associates the parameters in object parm to the distribution object.

A uniform_real_distribution is defined by two parameters: a and b, which specify the lower and upper bounds of the range of possible values generated by the distribution. An object of type param_type carries this information, but it is meant to be used only to construct or specify the parameters for a uniform_real_distribution object, not to inspect the individual parameters.